It is desirable if elongate frame members for vehicles can be axially collapsed in a manner so that impact energy is dissipated to protect the occupants of the vehicle during a collision or accident. To achieve increased dissipation of energy, frame members have been manufactured in the past with corrugations or fluting extending over a desired length of the frame member (see U.S. Pat. No. 3,811,698), with cuttings in the metal of the frame member to initiate the accordian-like crushing of the frame member (see U.S. Pat. No. 3,794,348), and with softened zones in the frame member brought about by annealing to promote corrugations (see U.S. Pat. No. 3,983,962).
These patents proceed on the theory that weakened zones of the frame member will initiate and multiply the deformation rate and thereby facilitate increased energy dissipation during the collapse of the frame member under heavy axial loading. However, the techniques of these particular patents provide insufficient dissipation of energy because the original structure being weakened inhibits absorption. In addition, the forming of the material with either fluting, cuttings or annealing zones presents difficult manufacturing problems in forming a desired configuration and in providing a desired profile in the frame member.
Other approaches to providing controlled dissipation of energy by collapse of a frame member are disclosed in U.S. Pat. No. 4,093,254 wherein a single fold is employed to provide the controlled collapse, in U.S. Pat. No. 3,795,410 wherein collapse is controlled to be at one locus, and in U.S. Pat. No. 3,981,114 wherein an inner column is inserted within the column to be controlled, but stationed to provide only a second phase of collapse. These represent an effort to isolate the crushing to a small zone so as to control the collapse capability of the structure but limiting energy absorption. Energy absorption is not maximized; less than 60% of the frame structure is collapsed during an axial loading condition.
Others have even ignored the problem of energy absorption by using precurved crush resistors which when inserted within the frame structure at curved portions work against any absorption at these particular zones with no intention of facilitating additional energy dissipation in other zones (see U.S. Pat. No. 3,827,712).